1. Field of the Invention
The present invention relates to a pipe coupling structure enabling pipe elements to be connected together without a gap between inner peripheral surfaces defining holes of the pipe elements.
2. Description of the Related Art
Flange coupling is typically used to connect pipes together in various piping systems. That is, flanges are provided on end portions of pipes to be connected together, and the flanges are abutted against each other and connected together by using nuts and bolts, or the flanges are connected together with a clamp tightened around the flanges.
In such flange coupling, a rubber seal ring is generally interposed between the flanges to seal therebetween in order to prevent leakage of gas or liquid from the inside of the piping system and to prevent contamination from the outside. The rubber seal ring, however, has various disadvantages. For example, sealing may become insufficient due to aging degradation of the rubber seal ring, or rubber as a packing material may get mixed in a fluid passed through the piping system. In case of a fire or the like, the rubber seal ring may be damaged by heat, resulting in incomplete sealing.
To solve the above-described problems, there has been proposed a technique to seal a joint part of a piping system without using a rubber seal ring (Patent Literature 1). With this technique, one of pipes to be joined together is provided at an end portion thereof with a tapered surface, and an end portion of the other of the pipes is pressed against the tapered surface. Alternatively, an annular metal packing is sandwiched between flanges on mutually opposing pipe end portions, and the mutually opposing flanges are pressed against tapered surfaces provided on both sides of the metal packing, thereby performing sealing by line contact between the metal members.
The above-described technique can realize excellent sealing performance without using a conventional rubber seal ring but has the problem that, when the coupling is repeatedly disassembled and reassembled, the tapered portions are likely to be damaged, and leakage is likely to occur.
Further, in such a pipe coupling, a recess is formed between a tapered surface provided on an end portion of one of the pipe elements, such as pipes and a metal packing, and a surface of an end portion of another pipe element pressed against the tapered surface. That is, when the pipe elements are connected together and a fluid passage is defined by the inner peripheral wall surfaces of the pipe elements, an annular groove (recess) is formed in the peripheral wall surface of the fluid passage at the pipe element joint part. In this regard, in a piping system for a fluid food, a fluid medicine, or the like where hygiene control is important, for example, the groove formed in the peripheral wall surface of the fluid passage as stated above is problematic because the food, medicine, or the like passed through the fluid passage enters the groove. Therefore, it is generally necessary to disassemble and wash the pipe coupling each time a production run is completed. However, a complicated operation is required to disassemble, wash and reassemble the pipe coupling for each production run, causing an increase in production cost.
Patent Literature 1: WO2004/10917